1. Field of the Invention
The present invention relates to bushings and more particularly to electrical bushings for connection with electrical apparatuses.
2. Description of the Prior Art
Various electrical bushings which include replaceable studs are known in the prior art for connection to electrical apparatuses. For example, U.S. Pat. No. 4,353,611 to Siebens et al. discloses a bushing well 42, a receptacle 41 in the bushing well 42, an electrical contact element 40 which is molded into the bushing well 42 and which includes an internally threaded hole 54, and a threaded rod 60 which threads into the hole 54. The rod 60 includes a wrenching socket 74 which extends therethrough, and an unthreaded extension 70 which jams against a portion 76 of the hole 54 to lock the element 40 and the rod 60 together.
U.S. Pat. No. 4,611,093 to Farmer et al. discloses an electrical bushing 10 which includes a bushing body 14 having a cavity 22 therein and a boss 24 projecting into the cavity 22. An electrical conductor 30 is located within the bushing body 14, has an upper end adjacent to and extending from an upper wall of the boss 24, and includes a threaded bore 34 therein. A replaceable stud 36 is also disclosed which includes a first threaded shank 38 threaded into the bore 34, a second threaded shank 40 opposite the first shank 38, and a flange 42 formed between the first and second shanks 38, 40 such that the flange 42 engages the upper wall of the boss 24 and the upper end of the conductor 30. The stud 36 is designed such that the diameter of the shank 38 is larger than the diameter of the shank 40, so that the shank 40 will break before the shank 38 to ensure removability of the stud 36 from the bore 34 after breakage of the stud 36.
Further, U.S. Pat. No. 4,782,197 to Stunzi et al. discloses an electrical bushing well 10 which includes a bushing 12 defining a bushing cavity in which a reentrant boss 24 is located. An electrical conductor 28, which includes a threaded bore 35, is molded into the bushing 12 such that a radially extending flange 34 of the conductor 28 overlies a shoulder portion of the reentrant boss 24. A replaceable stud 36 includes first and second threaded shanks 38, 40 and a central flange portion 42. In use, the second threaded shank 40 of the stud 36 is threaded into the bore 35 such that the central flange portion 42 is seated on the radially extending flange 34.
All three of the patents discussed above disclose bushings which include replaceable studs. Replaceable studs are known in the prior art as useful to prevent the expensive changing of an entire bushing when a conductive connector of the bushing breaks, since a replaceable stud can be designed to break before other parts of a bushing. However, each of the above patents has the disadvantage, among others, that it is relatively difficult for a person to reach into the cavity in the bushing well and correctly thread a replaceable stud into the conductor of the bushing. The cavities are generally designed to be relatively narrow and relatively deep, and may often be located in hard-to-reach places, thereby further compounding the problem. Incorrect threading can lead to the destruction of the leading threads of both a replaceable stud and a conductor of a bushing, which is both expensive, and costly in terms of the down-time required for replacement of a bushing.
Other electrical connections are known which include some type of connecting insert. For example, U.S. Pat. No. 4,799,895 to Borgstrom discloses, in FIGS. 6-10, a bushing 12, and a contact extender 290 which includes both an externally threaded stud 292 and an internally threaded recess 296, wherein the stud 292 is threaded into a conductor 62 in the bushing 12. Also, U.S. Pat. No. 4,955,823 to Luzzi discloses, in FIGS. 5 and 6, a bushing 20, and a contact extender 290 which includes both a male threaded portion 292 and a female threaded portion 296, wherein the male threaded portion 292 is threaded into a conductor of the bushing 20.
Further, U.S. Pat. No. 3,622,940 to Illies discloses, in FIG. 2, a connector assembly for an electrical apparatus which includes a shank portion 18 of a jack body, and a connector rod 17 embedded in the shank portion 18. A socket 16 has a shank 16a threaded into an internally threaded sleeve 17a which is connected to the connector rod 17 and is embedded in the shank portion 18.
These latter three patents, however, present the same disadvantage, among others, that the first three patents presented. The contact extenders of both of these patents would be susceptible to accidental cross-threading when the contact extenders are threaded into their respective bushings.
Other connectors are known which involve the threading of a female part onto a male part, instead of, or in addition to, the threading of a male part into a female part. For example, U.S. Pat. No. 1,856,001 to Spinelli discloses a spark plug which includes a center electrode 15 having male threads on a portion 17a thereof, a bushing 12 surrounding the portion 17a, and a sleeve 18. The sleeve 18 includes a male threaded terminal 18' on one end thereof, and a male and female threaded portion on an opposite end thereof which is threaded to the portion 17a and the bushing 12. A polygonal nut 18b is situated between the ends of the sleeve 18 for manipulation by a wrench.
Also, U.S. Pat. No. 2,397,097 to Forbes et al. discloses a separable connector bushing for an electrical apparatus. The bushing includes an insulating tubular member 1, and a stud 17 which is held in the member 1 and which includes a male screw-threaded end 19. A retainer nut 23 is internally threaded at 24 for threading to the end 19, and is externally threaded at 28.
These last two patents are also susceptible to cross-threading, among other disadvantages. Even though the devices of these patents involve the threading of a female part onto a male part, they are still subject to the possibility of cross-threading and its attendant disadvantages.